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- /* ----------------------------------------------------------------------
- * Copyright (C) 2010-2013 ARM Limited. All rights reserved.
- *
- * $Date: 17. January 2013
- * $Revision: V1.4.1
- *
- * Project: CMSIS DSP Library
- * Title: arm_fir_decimate_f32.c
- *
- * Description: FIR decimation for floating-point sequences.
- *
- * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * - Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- * - Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in
- * the documentation and/or other materials provided with the
- * distribution.
- * - Neither the name of ARM LIMITED nor the names of its contributors
- * may be used to endorse or promote products derived from this
- * software without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
- * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
- * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
- * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
- * POSSIBILITY OF SUCH DAMAGE.
- * -------------------------------------------------------------------- */
-
- #include "arm_math.h"
-
- /**
- * @ingroup groupFilters
- */
-
- /**
- * @defgroup FIR_decimate Finite Impulse Response (FIR) Decimator
- *
- * These functions combine an FIR filter together with a decimator.
- * They are used in multirate systems for reducing the sample rate of a signal without introducing aliasing distortion.
- * Conceptually, the functions are equivalent to the block diagram below:
- * \image html FIRDecimator.gif "Components included in the FIR Decimator functions"
- * When decimating by a factor of <code>M</code>, the signal should be prefiltered by a lowpass filter with a normalized
- * cutoff frequency of <code>1/M</code> in order to prevent aliasing distortion.
- * The user of the function is responsible for providing the filter coefficients.
- *
- * The FIR decimator functions provided in the CMSIS DSP Library combine the FIR filter and the decimator in an efficient manner.
- * Instead of calculating all of the FIR filter outputs and discarding <code>M-1</code> out of every <code>M</code>, only the
- * samples output by the decimator are computed.
- * The functions operate on blocks of input and output data.
- * <code>pSrc</code> points to an array of <code>blockSize</code> input values and
- * <code>pDst</code> points to an array of <code>blockSize/M</code> output values.
- * In order to have an integer number of output samples <code>blockSize</code>
- * must always be a multiple of the decimation factor <code>M</code>.
- *
- * The library provides separate functions for Q15, Q31 and floating-point data types.
- *
- * \par Algorithm:
- * The FIR portion of the algorithm uses the standard form filter:
- * <pre>
- * y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1]
- * </pre>
- * where, <code>b[n]</code> are the filter coefficients.
- * \par
- * The <code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>.
- * Coefficients are stored in time reversed order.
- * \par
- * <pre>
- * {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
- * </pre>
- * \par
- * <code>pState</code> points to a state array of size <code>numTaps + blockSize - 1</code>.
- * Samples in the state buffer are stored in the order:
- * \par
- * <pre>
- * {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]}
- * </pre>
- * The state variables are updated after each block of data is processed, the coefficients are untouched.
- *
- * \par Instance Structure
- * The coefficients and state variables for a filter are stored together in an instance data structure.
- * A separate instance structure must be defined for each filter.
- * Coefficient arrays may be shared among several instances while state variable array should be allocated separately.
- * There are separate instance structure declarations for each of the 3 supported data types.
- *
- * \par Initialization Functions
- * There is also an associated initialization function for each data type.
- * The initialization function performs the following operations:
- * - Sets the values of the internal structure fields.
- * - Zeros out the values in the state buffer.
- * - Checks to make sure that the size of the input is a multiple of the decimation factor.
- * To do this manually without calling the init function, assign the follow subfields of the instance structure:
- * numTaps, pCoeffs, M (decimation factor), pState. Also set all of the values in pState to zero.
- *
- * \par
- * Use of the initialization function is optional.
- * However, if the initialization function is used, then the instance structure cannot be placed into a const data section.
- * To place an instance structure into a const data section, the instance structure must be manually initialized.
- * The code below statically initializes each of the 3 different data type filter instance structures
- * <pre>
- *arm_fir_decimate_instance_f32 S = {M, numTaps, pCoeffs, pState};
- *arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState};
- *arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState};
- * </pre>
- * where <code>M</code> is the decimation factor; <code>numTaps</code> is the number of filter coefficients in the filter;
- * <code>pCoeffs</code> is the address of the coefficient buffer;
- * <code>pState</code> is the address of the state buffer.
- * Be sure to set the values in the state buffer to zeros when doing static initialization.
- *
- * \par Fixed-Point Behavior
- * Care must be taken when using the fixed-point versions of the FIR decimate filter functions.
- * In particular, the overflow and saturation behavior of the accumulator used in each function must be considered.
- * Refer to the function specific documentation below for usage guidelines.
- */
-
- /**
- * @addtogroup FIR_decimate
- * @{
- */
-
- /**
- * @brief Processing function for the floating-point FIR decimator.
- * @param[in] *S points to an instance of the floating-point FIR decimator structure.
- * @param[in] *pSrc points to the block of input data.
- * @param[out] *pDst points to the block of output data.
- * @param[in] blockSize number of input samples to process per call.
- * @return none.
- */
-
- void arm_fir_decimate_f32(
- const arm_fir_decimate_instance_f32 * S,
- float32_t * pSrc,
- float32_t * pDst,
- uint32_t blockSize)
- {
- float32_t *pState = S->pState; /* State pointer */
- float32_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
- float32_t *pStateCurnt; /* Points to the current sample of the state */
- float32_t *px, *pb; /* Temporary pointers for state and coefficient buffers */
- float32_t sum0; /* Accumulator */
- float32_t x0, c0; /* Temporary variables to hold state and coefficient values */
- uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */
- uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */
-
- #ifndef ARM_MATH_CM0_FAMILY
-
- uint32_t blkCntN4;
- float32_t *px0, *px1, *px2, *px3;
- float32_t acc0, acc1, acc2, acc3;
- float32_t x1, x2, x3;
-
- /* Run the below code for Cortex-M4 and Cortex-M3 */
-
- /* S->pState buffer contains previous frame (numTaps - 1) samples */
- /* pStateCurnt points to the location where the new input data should be written */
- pStateCurnt = S->pState + (numTaps - 1u);
-
- /* Total number of output samples to be computed */
- blkCnt = outBlockSize / 4;
- blkCntN4 = outBlockSize - (4 * blkCnt);
-
- while(blkCnt > 0u)
- {
- /* Copy 4 * decimation factor number of new input samples into the state buffer */
- i = 4 * S->M;
-
- do
- {
- *pStateCurnt++ = *pSrc++;
-
- } while(--i);
-
- /* Set accumulators to zero */
- acc0 = 0.0f;
- acc1 = 0.0f;
- acc2 = 0.0f;
- acc3 = 0.0f;
-
- /* Initialize state pointer for all the samples */
- px0 = pState;
- px1 = pState + S->M;
- px2 = pState + 2 * S->M;
- px3 = pState + 3 * S->M;
-
- /* Initialize coeff pointer */
- pb = pCoeffs;
-
- /* Loop unrolling. Process 4 taps at a time. */
- tapCnt = numTaps >> 2;
-
- /* Loop over the number of taps. Unroll by a factor of 4.
- ** Repeat until we've computed numTaps-4 coefficients. */
-
- while(tapCnt > 0u)
- {
- /* Read the b[numTaps-1] coefficient */
- c0 = *(pb++);
-
- /* Read x[n-numTaps-1] sample for acc0 */
- x0 = *(px0++);
- /* Read x[n-numTaps-1] sample for acc1 */
- x1 = *(px1++);
- /* Read x[n-numTaps-1] sample for acc2 */
- x2 = *(px2++);
- /* Read x[n-numTaps-1] sample for acc3 */
- x3 = *(px3++);
-
- /* Perform the multiply-accumulate */
- acc0 += x0 * c0;
- acc1 += x1 * c0;
- acc2 += x2 * c0;
- acc3 += x3 * c0;
-
- /* Read the b[numTaps-2] coefficient */
- c0 = *(pb++);
-
- /* Read x[n-numTaps-2] sample for acc0, acc1, acc2, acc3 */
- x0 = *(px0++);
- x1 = *(px1++);
- x2 = *(px2++);
- x3 = *(px3++);
-
- /* Perform the multiply-accumulate */
- acc0 += x0 * c0;
- acc1 += x1 * c0;
- acc2 += x2 * c0;
- acc3 += x3 * c0;
-
- /* Read the b[numTaps-3] coefficient */
- c0 = *(pb++);
-
- /* Read x[n-numTaps-3] sample acc0, acc1, acc2, acc3 */
- x0 = *(px0++);
- x1 = *(px1++);
- x2 = *(px2++);
- x3 = *(px3++);
-
- /* Perform the multiply-accumulate */
- acc0 += x0 * c0;
- acc1 += x1 * c0;
- acc2 += x2 * c0;
- acc3 += x3 * c0;
-
- /* Read the b[numTaps-4] coefficient */
- c0 = *(pb++);
-
- /* Read x[n-numTaps-4] sample acc0, acc1, acc2, acc3 */
- x0 = *(px0++);
- x1 = *(px1++);
- x2 = *(px2++);
- x3 = *(px3++);
-
- /* Perform the multiply-accumulate */
- acc0 += x0 * c0;
- acc1 += x1 * c0;
- acc2 += x2 * c0;
- acc3 += x3 * c0;
-
- /* Decrement the loop counter */
- tapCnt--;
- }
-
- /* If the filter length is not a multiple of 4, compute the remaining filter taps */
- tapCnt = numTaps % 0x4u;
-
- while(tapCnt > 0u)
- {
- /* Read coefficients */
- c0 = *(pb++);
-
- /* Fetch state variables for acc0, acc1, acc2, acc3 */
- x0 = *(px0++);
- x1 = *(px1++);
- x2 = *(px2++);
- x3 = *(px3++);
-
- /* Perform the multiply-accumulate */
- acc0 += x0 * c0;
- acc1 += x1 * c0;
- acc2 += x2 * c0;
- acc3 += x3 * c0;
-
- /* Decrement the loop counter */
- tapCnt--;
- }
-
- /* Advance the state pointer by the decimation factor
- * to process the next group of decimation factor number samples */
- pState = pState + 4 * S->M;
-
- /* The result is in the accumulator, store in the destination buffer. */
- *pDst++ = acc0;
- *pDst++ = acc1;
- *pDst++ = acc2;
- *pDst++ = acc3;
-
- /* Decrement the loop counter */
- blkCnt--;
- }
-
- while(blkCntN4 > 0u)
- {
- /* Copy decimation factor number of new input samples into the state buffer */
- i = S->M;
-
- do
- {
- *pStateCurnt++ = *pSrc++;
-
- } while(--i);
-
- /* Set accumulator to zero */
- sum0 = 0.0f;
-
- /* Initialize state pointer */
- px = pState;
-
- /* Initialize coeff pointer */
- pb = pCoeffs;
-
- /* Loop unrolling. Process 4 taps at a time. */
- tapCnt = numTaps >> 2;
-
- /* Loop over the number of taps. Unroll by a factor of 4.
- ** Repeat until we've computed numTaps-4 coefficients. */
- while(tapCnt > 0u)
- {
- /* Read the b[numTaps-1] coefficient */
- c0 = *(pb++);
-
- /* Read x[n-numTaps-1] sample */
- x0 = *(px++);
-
- /* Perform the multiply-accumulate */
- sum0 += x0 * c0;
-
- /* Read the b[numTaps-2] coefficient */
- c0 = *(pb++);
-
- /* Read x[n-numTaps-2] sample */
- x0 = *(px++);
-
- /* Perform the multiply-accumulate */
- sum0 += x0 * c0;
-
- /* Read the b[numTaps-3] coefficient */
- c0 = *(pb++);
-
- /* Read x[n-numTaps-3] sample */
- x0 = *(px++);
-
- /* Perform the multiply-accumulate */
- sum0 += x0 * c0;
-
- /* Read the b[numTaps-4] coefficient */
- c0 = *(pb++);
-
- /* Read x[n-numTaps-4] sample */
- x0 = *(px++);
-
- /* Perform the multiply-accumulate */
- sum0 += x0 * c0;
-
- /* Decrement the loop counter */
- tapCnt--;
- }
-
- /* If the filter length is not a multiple of 4, compute the remaining filter taps */
- tapCnt = numTaps % 0x4u;
-
- while(tapCnt > 0u)
- {
- /* Read coefficients */
- c0 = *(pb++);
-
- /* Fetch 1 state variable */
- x0 = *(px++);
-
- /* Perform the multiply-accumulate */
- sum0 += x0 * c0;
-
- /* Decrement the loop counter */
- tapCnt--;
- }
-
- /* Advance the state pointer by the decimation factor
- * to process the next group of decimation factor number samples */
- pState = pState + S->M;
-
- /* The result is in the accumulator, store in the destination buffer. */
- *pDst++ = sum0;
-
- /* Decrement the loop counter */
- blkCntN4--;
- }
-
- /* Processing is complete.
- ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
- ** This prepares the state buffer for the next function call. */
-
- /* Points to the start of the state buffer */
- pStateCurnt = S->pState;
-
- i = (numTaps - 1u) >> 2;
-
- /* copy data */
- while(i > 0u)
- {
- *pStateCurnt++ = *pState++;
- *pStateCurnt++ = *pState++;
- *pStateCurnt++ = *pState++;
- *pStateCurnt++ = *pState++;
-
- /* Decrement the loop counter */
- i--;
- }
-
- i = (numTaps - 1u) % 0x04u;
-
- /* copy data */
- while(i > 0u)
- {
- *pStateCurnt++ = *pState++;
-
- /* Decrement the loop counter */
- i--;
- }
-
- #else
-
- /* Run the below code for Cortex-M0 */
-
- /* S->pState buffer contains previous frame (numTaps - 1) samples */
- /* pStateCurnt points to the location where the new input data should be written */
- pStateCurnt = S->pState + (numTaps - 1u);
-
- /* Total number of output samples to be computed */
- blkCnt = outBlockSize;
-
- while(blkCnt > 0u)
- {
- /* Copy decimation factor number of new input samples into the state buffer */
- i = S->M;
-
- do
- {
- *pStateCurnt++ = *pSrc++;
-
- } while(--i);
-
- /* Set accumulator to zero */
- sum0 = 0.0f;
-
- /* Initialize state pointer */
- px = pState;
-
- /* Initialize coeff pointer */
- pb = pCoeffs;
-
- tapCnt = numTaps;
-
- while(tapCnt > 0u)
- {
- /* Read coefficients */
- c0 = *pb++;
-
- /* Fetch 1 state variable */
- x0 = *px++;
-
- /* Perform the multiply-accumulate */
- sum0 += x0 * c0;
-
- /* Decrement the loop counter */
- tapCnt--;
- }
-
- /* Advance the state pointer by the decimation factor
- * to process the next group of decimation factor number samples */
- pState = pState + S->M;
-
- /* The result is in the accumulator, store in the destination buffer. */
- *pDst++ = sum0;
-
- /* Decrement the loop counter */
- blkCnt--;
- }
-
- /* Processing is complete.
- ** Now copy the last numTaps - 1 samples to the start of the state buffer.
- ** This prepares the state buffer for the next function call. */
-
- /* Points to the start of the state buffer */
- pStateCurnt = S->pState;
-
- /* Copy numTaps number of values */
- i = (numTaps - 1u);
-
- /* copy data */
- while(i > 0u)
- {
- *pStateCurnt++ = *pState++;
-
- /* Decrement the loop counter */
- i--;
- }
-
- #endif /* #ifndef ARM_MATH_CM0_FAMILY */
-
- }
-
- /**
- * @} end of FIR_decimate group
- */
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